Gamma-Emitting States inO16below 12 Mev

A study has been made of states in ${\mathrm{O}}^{16}$ between 7.2- and 11.5-Mev excitation which belong to the sequence $0^{-}$, $1^{+}$, $2^{-}$, $3^{+}$,... (even angular momentum and odd parity, and vice versa). These states cannot break up into ${\mathrm{C}}^{12}$+$\alpha$ but must decay by $\gamma$ emission. The $\gamma$ rays from the ${\mathrm{F}}^{19}(p, \alpha \gamma ){\mathrm{O}}^{16}$ and ${\mathrm{N}}^{15}(d, n\gamma ){\mathrm{O}}^{16}$ reactions were studied at bombarding energies up to 6.0 and 5.08 Mev, respectively, using a three-crystal pair spectrometer and other scintillation counters. The design, resolution, and efficiency of the three-crystal pair spectrometer are given. The ground state transition from the $2^{-}$, 8.87-Mev state was observed to have 0.07±0.02 the intensity of the 2.73-Mev cascade transition to the $3^{-}$, 6.14-Mev state. A state was found at 10.98±0.04 Mev which decays predominantly to the $1^{-}$, 7.12-Mev state. No $\gamma$ rays resulting from the decay of this state to other states of ${\mathrm{O}}^{16}$ were observed. The angular correlation of the 3.86- and 7.12-Mev $\gamma$ rays shows a positive anisotropy of approximately 1. These results suggest a $0^{-}$ spin and parity assignment for the 10.98-Mev state. The predictions of the alpha-particle and shell models of ${\mathrm{O}}^{16}$ are compared with these results.